1. Technical Field
The present disclosure relates to a method and apparatus for forming a carbon nanotube array.
2. Description of Related Art
A carbon nanotube array is grown on a flat silicon wafer by using a chemical vapor deposition (CVD) method. More specifically, a layer of nanosized catalyst grains is arranged on the flat silicon wafer by annealing a metal film deposited on the wafer. Then the wafer is disposed and heated in a reactor chamber. Carbon source gas and protective gas are introduced into the reactor chamber and the carbon source gas is pyrolyzed by an action of the catalyst grains at elevated temperature to grow the carbon nanotube array on the flat silicon wafer. However, the size of the carbon nanotube array grown on the flat silicon wafer is restricted by the size of the reactor chamber.
Recently, a method for growing a large-area carbon nanotube film is disclosed by the patent application US20070292614 A1 to Liu et al. The method includes steps of: providing a cylinder shaped substrate; forming a catalyst layer on the outer surface of the cylinder shaped substrate; fixing the cylinder shaped substrate in a reactor chamber; and growing a carbon nanotube film on the outer surface of the cylinder shaped substrate by the CVD process. The silicon wafer and the cylinder shaped substrate with the same diameter that can be accommodated by the same reactor chamber, can have different surface area that has the carbon nanotubes grown thereon, wherein the outer surface of the cylinder shaped substrate is larger than the flat surface of the silicon wafer. Therefore, a larger carbon nanotube film can be achieved by using the cylinder shaped substrate but not to increase the size of the reactor chamber, especially not increase a diameter of a tube furnace.
However, in the above method, the reactor chamber is heated to 700° C. by resistance wires coiled outside the reactor chamber, to indirectly heat the cylinder shaped substrate thereby pyrolyzing the carbon source gas. When the carbon nanotubes have been grown on the outer surface of the cylinder shaped substrate, an amount of heat is absorbed by the carbon nanotubes to slow down the heating speed of the substrate and the growing speed of the carbon nanotubes. As the increasing of the height of the carbon nanotubes, the growing speed of the carbon nanotubes becomes slower.
What is needed, therefore, is to provide a method and an apparatus for forming a carbon nanotube array at a quickly growing speed.